1. Field of the Invention
The present invention relates to a system and method for writing servo sectors in a perpendicular media recording (PMR) environment to a disk.
2. Description of the Prior Art and Related Information
Today, computing devices such as personal computers, personal digital assistants, cell-phones, etc., are routinely used at work, at home, and everywhere in-between. Computing devices advantageously enable the use of application specific software, file sharing, the creation of electronic documents, and electronic communication and commerce through the Internet and other computer networks. Typically, each computing device has a storage peripheral such as a disk drive.
A huge market exists for disk drives for mass-market computing devices such as desktop computers and laptop computers, as well as small form factor (SFF) disk drives for use in mobile computing devices (e.g. personal digital assistants (PDAs), cell-phones, digital cameras, etc.). To be competitive, a disk drive should be relatively inexpensive and provide substantial capacity, rapid access to data, and reliable performance.
Disk drives typically employ a moveable head actuator to frequently access large amounts of data stored on a disk. One example of a disk drive is a hard disk drive. A conventional hard disk drive has a head disk assembly (“HDA”) including at least one magnetic disk (“disk”), a spindle motor for rapidly rotating the disk, and a head stack assembly (“HSA”) that includes a head gimbal assembly (HGA) with a moveable transducer head for reading and writing data. The HSA forms part of a servo control system that positions the moveable transducer head over a particular track on the disk to read or write information from and to that track, respectively.
Typically, a conventional hard disk drive includes a disk having a plurality of concentric tracks. Each surface of each disk conventionally contains a plurality of concentric data tracks angularly divided into a plurality of data sectors. In addition, special servo information may be provided on each disk to determine the position of the moveable transducer head.
The most popular form of servo is called “embedded servo” wherein the servo information is written in a plurality of servo sectors that are angularly spaced from one another and are interspersed between data sectors around each track of each disk.
Each servo sector typically includes a phase lock loop (PLL) field, a servo synch mark (SSM) field, a gray-coded track identification (TKID), a sector ID field having a binary encoded sector ID number to identify the sector, and a group of servo bursts (e.g. an alternating pattern of magnetic transitions) which the servo control system of the disk drive samples to align the moveable transducer head with or relative to a particular track. Typically, the servo control system moves the transducer head toward a desired track during a “seek” mode using the gray-coded TKID field as a control input.
When manufacturing a disk drive, the servo sectors are typically written to the disk in order to define a plurality of evenly-spaced, concentric tracks. As previously discussed, a typical servo sector includes a PLL field, a SSM field, a gray-coded TKID field, and a sector ID field.
Servo writers are typically used to write the servo sectors to the disk surface during disk drive manufacturing. Servo writers may employ extremely accurate head positioning mechanics, such as laser interferometers or optical encoders, to ensure that the servo sectors are written at the proper radial location, typically, from the inner diameter of the disk to the outer diameter of the disk. In addition, extremely accurate clocking systems may be utilized in order to write the servo sectors in the proper circumferential locations on the disk. Servo-writing may occur both in-situ utilizing the disk drive itself or just the HDA of the disk drive to write the servo-sectors, or servo-writing may be performed on a disk in an external environment.
As previously discussed, the disk drive industry is very competitive and disk drives are continually being sought after by consumers that provide substantial capacity and rapid access to data. In order to meet consumer demand for increased capacity and faster access to data, a new form of media recording, entitled perpendicular media recording (PMR) is now being utilized in order to increase the amount of data that can be stored on a disk.
Perpendicular media recording (PMR) allows hard disk drive manufacturers to put more bits of data on each square inch of disk because of magnetic geometry. In perpendicular media recording, writing on the magnetic media occurs in a fashion in which the bits are aligned vertically, perpendicular to the disk, rather than parallel to the media, as is currently done. By writing bits of data in a vertical fashion, higher recording densities on the disk are enabled because bits of data can be packed closer together.
Further, by utilizing perpendicular media recording (PMR) an improvement results in that bits are better able to retain their magnetic charges, a property called coercivity. This helps to alleviate the “flipped bit” problem associated with standard parallel recording techniques. Due to the ever increasing bit density provided on disk media utilizing standard parallel recording techniques, bits are being written closer and closer together to improve disk density, such that when random thermal vibrations occur bits may be “flipped”—in which the magnetic north and south poles of bits are suddenly and spontaneously reversed, resulting in corrupted data.
Although perpendicular media recording (PMR) offers vast advantages in the amount and reliability of data that can be stored on a disk of a disk drive, there is presently a problem in servo writing disks utilizing PMR technology due to the PMR disk head's footprint and sensitivity to skew angle in writing servo sectors to a disk.
For example, in utilizing conventional servo writing techniques with a PMR head, servo writing typically occurs in a single direction. Unfortunately, a problem occurs in that the written-in servo sectors may become unreadable at large skew angles due to the footprint of the PMR head. For example, when servo-writing in a single direction from the inner diameter (ID) of the disk to the outer diameter (OD) of the disk, as is commonly done, servo sectors may become unreadable at the OD side of the disk.
More particularly, when servo-writing in a single direction utilizing a PMR head, at large skew angles, written-in servo sectors and the gray coded TKIDs contained therein used for seek operations may become unreadable resulting in wasted disk space and potential problems for disk drive operations.